[Nosology and mechanism of monomorphous atrial tachycardia].

Monomorphous atrial tachycardias have been classified taking into account the ectopic rhythm rate, atrial wave morphology, the mode of activation of the atrial studied by endocavitary cartography, stimulation tests and their natural history. Atrial flutter is a right intra-atrial macroreentry of anticlockwise (common flutter) or clockwise (atypical flutter) rotation, maintained by anisotropic conduction around two pivotal zones located at the posterior and inferior part of the atrium. Tachycardia is made possible by the existence of an excitable zone on the circuit. Paroxysmal atrial tachycardias are far more often linked to localised reentry (sino-atrial or intra-atrial microreentry) than to provoked activity, stimulation tests enabling the distinction to be made. "Digitalis tachycardias" must be seen in the context of activity induced by late post-potential. Focal atrial tachycardias linked to ectopic automatism are a separate entity. They follow a chronic course in the young individual and may lead to a cardiomyopathy purely due to the rhythm abnormality.